The present invention relates to electric vehicles with automatic transmissions and in particular to a new, improved method of controlling the actuation of a multi-speed transmission implementing one or more clutches.
Known electric vehicles with multi-speed transmissions select a transmission ratio by engaging one of two or more clutches or positively ganging members. Either of these methods generally result in frictional drag on the system due to the disengaged clutches. U.S. Provisional Patent Application Ser. No. 61/099908 filed Sep. 25, 2008 by the present inventor and incorporated herein by reference, describes an improved clutch mechanism to reduced drag on a multi-speed transmission. While the '908 application provides reduced drag, it does not disclose an optimal method to efficiently disengage and engage the clutches at the proper times to minimized the time of clutch disengagement, the duration between shifts, and the wear on the drive system, and does not attempt to maximize the smoothness of the operation.
Additionally, disengagement of a lower ratio clutch and the subsequent engagement of a higher ratio clutch is not instantaneous and results in a period of time with no power being coupled to the drive wheels. This may results in jarring the vehicle and be an annoyance to the operator.